1. Field of the Invention
The present invention relates to refrigerator cabinets and, more particularly, to a door frame structure for use with such cabinets.
2. Description of the Prior Art
Contemporary refrigerated cabinets are usually provided with doors having a large window area to enhance the display characteristics of the refrigerator. U.S. Pat. No. 3,724,129 to Stromquist, issued Apr. 3, 1973, shows a door frame of the contemporary type. The door is typically fabricated from a multi-pane glass panel which in turn is mounted in a metal supporting door frame.
The metal supporting frame is supplied with a gasket for forming a seal between the door frame and the frame in which the door is mounted. The front face of the door is surrounded by air at room temperature, while the inner face of the door is exposed to the cold air inside the refrigerator. Heat is absorbed by conduction from the air outside the refrigerator and is conducted through the metallic door frame around the edge of the door and into the cold portion of the door frame which is in contact with the cold air inside the refrigerator.
A temperature gradient exists from the warm portion of the door frame around the edge of the door and into the cold portion of the door frame. Because the door frame is typically made of metal, such as aluminum, rather large amounts of heat can enter the refrigerator by this conductive path, resulting in a great waste of energy and higher operating costs.
It is desirable to provide means for reducing the flow of heat from the warm portion of the door frame to the colder portion of the door frame to reduce the energy expended to maintain the refrigerated environment. One approach to this would be to simply construct the door frame from a material of relatively low thermal conductivity. This approach has not met with commercial success at this time because of the high cost of suitable materials.
In U.S. Pat. No. 3,204,324, issued Sept. 7, 1965, Nilsen shows a method for producing an insulating construction for structural members for use in window frames and like structures wherein the structural members on the warm and cold sides of the structural member are separated by an insulating spacer. That method includes providing originally a metal strip having a channel into which solidifiable insulative material is poured and allowed to solidify, then removing a part of the original strip forming the channel. This leaves a final structure consisting of two parts of the original strip bonded to the insulative material but spaced apart from each other by it, whereby the thermally conductive path between the two parts is interrupted by the insulative material. Nilsen, nowhere suggests use of the structural member formed by his method in a door frame for a refrigerator, and it will be seen that his structures are not totally suitable when applied to refrigerator door frames.
The applicability of the Nilsen technique to a door frame for a refrigerator is greatly complicated by the unique design constraints placed upon the refrigerator door frame. It is contemplated that the door frame construction of the present invention will preferably be used to form the entire periphery of the door. It is known in the art to pivot such doors from a torque-producing hinge pin to urge the door shut. The use of such a hinge pin results in large torques being applied to the central portion of the vertical door frame on the hinged side of the door. Likewise, the vertical door frame member to which the handle is normally attached is subject to repeated mechanical shock when the door is slammed shut in normal use. To reliably withstand these mechanical stresses, a refrigerator door frame using an insulative strip must be carefully conceived.
A second design constraint inherent in the refrigerator door frame is that those portions of the frame normally visible to the public must present an aesthetically clean and solid appearance. For this reason a structure is desired which enables placement of the insulative strip where it cannot readily be seen by the public.
In modern refrigerator doors the sealing means is not located on the edge of the door, but rather on the inner face of the door near its periphery. The temperature transition from cold to warm takes place in the vicinity of the seal. Therefore, if the insulative section were disposed across the central portion of the U-shaped frame member, a sizeable portion of the flange running along the inner face of the door would be exposed to the warm air outside the refrigerator, while another portion of the same flange would be exposed to the cold air inside the refrigerator. This would defeat the purpose of the insulative barrier, because heat would flow from the warm portion to the cold portion of the flange.
It is well known in the art to provide heater wires within the door frame to prevent the formation of condensation and frost on it. This was necessitated by the relatively good thermal path which prior art door frames provided, permitting heat to flow readily from the warmer outer portion of the frame into the portion of the door frame normally exposed to the cold air inside the refrigerator. The use of heater wires compounded the inefficiency of the unit, consuming electricity to supply additional heat to the colder portion of the door frame. It is an objective of the present invention to provide such an efficient door frame structure that the use of heater wires is unnecessary except under extreme conditions.